(Studies suggest that nightlight use by children
does not increase the risk of
nearsightedness)

March 28, 2000

The Past

On May 28, 1999, a Neuroscience for Kids, In the News page reported on a
research study that suggested that children who used nightlights were at a
greater risk of becoming nearsighted than those who did not use
nightlights. This study showed that only 10% of the children who slept in
darkness were nearsighted compared with 34% of the children who slept with
a nightlight and 55% of the children who slept with a room light and later
developed nearsightedness.

New Data

Two studies (both published in Nature, March 9, 2000)
show that using nightlights may NOT contribute to nearsightedness. In the
first
study, scientists studied 1,220 children (median age, 10.2 years old).
The number of
children who were nearsighted was approximately the same in different
lighting conditions: 20% of the children (84 of 417 children) who slept
in darkness were nearsighted; 16.8% of the children (128 of 758 children)
who slept with a nightlight before they were two years old were
nearsighted; 22.2% of the children (10 of 45 children) who sleep with the
room lights on were nearsighted.

The second study examined the incidence of nearsightedness in 213 children
(mean age, 10 years old) and their parents. Again, as in the other study,
the use of nightlights did not change the probability of becoming
nearsighted: 20% of the children who slept with a nightlight before the
age of 2 years were nearsighted; 20% of the children who slept in the dark
were nearsighted and none of the children who slept with room lights on
were nearsighted. Nightlights were used more often when both parents were
nearsighted. Also, if both parent were nearsighted, the children were
more likely to be nearsighted themselves compared to children with either
one nearsighted parent or no nearsighted parents.

Data from:

Quinn et al., 1999

Zadnik et al.,
2000

Gwiazda et al., 2000

Why The Difference Between Studies?

The studies appear to
contradict the earlier study and suggest that using a nightlight does NOT
contribute to nearsightedness. Rather, these data suggest that
nearsightedness is related to something inherited from parents. Two
reasons may explain the differences between the results of the old and new
research:

The study published in 1999 did not ask parents if
they were nearsighted and therefore, this important piece of information
was missing.

The authors of the 1999 study, in a letter published
in Nature, argue that parents may not have answered questions
truthfully in the new studies. They point out that their original study
received extensive press coverage warning about the potential problem with
nightlights. They believe that parents may have felt guilty about using
nightlights and may not have admitted to researchers that their children
used nightlights.

So, do nightlights contribute to nearsightedness or not? This research
makes the case that heredity plays a strong role in the development of
nearsightedness. The older study failed to consider the possibility of a
genetic factor. Did parents in the new studies answer questions
truthfully? Future research may provide us with more certain
answers.